The city wants people to stop piling stones at the mouth of a storm drain, saying it prevents the drain from working as it should.

City workers Tim Powis, left, and Dax McAllister clear rocks from the mouth of a storm drain in the Gainsborough ravine, which were put in the tiny stream that feeds it by area residents to catch debris.

Rocks piled by residents at the mouth of a storm drain in a ravine to catch debris are causing even more junk to clog it, Toronto Water says.

On May 13 we reported that area residents and the city were working at odds to prevent debris from plugging a large storm drain fed by a tiny stream in the Gainsborough ravine, near Coxwell Ave. and Gerrard St.

Residents pile rocks into the stream to keep debris out of the drain, which Justin Gobel, who first told us about it, says is a better fix than anything the city has come up with.

But Ralph Vogel, a Toronto Water supervisor, says rocks in the stream prevent the drain from working as it was designed and only make matters worse, which is why the city keeps removing them.

We went to the ravine to meet Vogel and two Toronto Water employees who were hauling rocks out of the stream, and got a demonstration of how debris ends up in the drain because of them.

“The residents have the best intentions but don’t understand the design,” he said, adding that when the water is higher after a rainfall, the rocks reroute it, along with any debris carried along in it.

A grate at the entrance to the drain, or “inlet,” is designed to catch debris, which is regularly removed by workers who keep an eye on the accumulation, he said.

When debris is caught by the rocks, high water rushing around it eventually carries the junk toward a box-shaped screen made of chain-link fencing that surrounds the drain, said Vogel.

Instead of piling up around the grate at the entrance to the drain, the debris washes into it through weak spots in the fencing, which can worsen flooding in the floor of the ravine, he said.

“The inlet is designed to catch the large material, and our job is to remove it,” said Vogel. “The rocks cause debris to wash up and around the screen, which is only a safety measure and not meant to catch debris.”

It sounds reasonable, but does not square with the experience of people who swear it works the other way around, which means the rock fight is likely to continue.

What’s broken in your neighbourhood? Wherever you are in Greater Toronto, we want to know. To email us, go to www.thestar.com/thefixer and click on the submit a problem link. Or call us at 416-869-4823.

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